In its International Energy Outlook for 2008, the Energy Information Administration forecast that global energy consumption will grow by 50% between 2005 and 2030. Total global transportation fuel production is expected to reach 93 millions barrels of oil per day (MMbbl/d) by 2020. It is expected that coal-to-liquid (CTL) will become increasingly necessary to compensate for the increase in oil consumption. World production of unconventional resources (coal-to-liquid, gas-to-liquid, etc) totaled only 2.5 MMbbl/d in 2005, yet is expected to increase to at least 9.7 MMbbl/d by 2030, accounting for 9% of the total world liquid supply on an oil-equivalent basis.
Promising prospects are also predicted for other industrial gasification processes including turning vast world reserves of coal, oil sands, waste coal and petcoke into an array of higher value products such as electrical power, liquid fuels, SNG, fertilizers and other chemical feed stocks. High oil and gas prices make this a virtually irresistible option.
Because many of these industrial processes use large quantities of energy and are therefore costly, efforts are made to recover as much as possible of wasted energy, which is often in the form of heat. Hence, it is known to use power generation plants to recover waste energy during these industrial processes.
For example, processes with entrained flow gasifiers or other exothermal reactors are often characterized by the generation of large quantities of waste heat, which may be at least partly transferred to saturated steam at various pressures according to the location in the process. In a typical CTL plant using gasifiers and producing 40,000 bbl/d, a waste heat boiler and a Fischer-Tropsch (F-T) reactor, each produce approximately 1,000 tonne/h of saturated steam that can be used for power generation.
In a conventional power generation plant, each source of saturated steam is superheated in its own fired superheater before being fed to conventional steam turbines. The fuel used to fire the superheaters is usually a fuel gas purged from a synthesis loop of the industrial process. However, the fired superheaters are expensive pieces of equipment, their efficiency is poor, and they are sources of air polluting emissions.
Considering the quantity of waste energy involved in CTL and various other industrial processes, it is clear that improving the efficiency of the power generation process, or of one of its steps, can lead to significant additional energy recovery. Moreover, in view of ever increasing environmental considerations, improvements in the efficiency of the power generation process and plant are clearly advantageous.